The invention resides in a press with a press drive, for example, for the manufacture of metal sheet parts or for the deformation of massive metal components.
In the present state of the art, in the deformation of metal sheets for same time, mechanically driven presses with fly wheel drives have been used. In such presses, the travel-time curve of the plunger as generated by the kinematics of the drive which transmits the drive energy of the fly wheel to the plunger is predetermined. Changes in the travel-drive curve are only possible in connection with a stroke change. The striving for more productive manufacturing processes and the continually increasing requirements in the drawing processes resulted lately in the use of so-called servo presses in the shaping of sheet metal parts.
These servo presses are equipped with variable servo drives capable of generating different press forces. These presses are driven by one or several servomotors, which act directly on the drive train, without a fly wheel and without a clutch. In servo presses with relatively large press forces, high-moment torque motors are often used. With respect to speed and direction of rotation these motors can be controlled in a flexible manner so that they are programmable for different travel-time curves of the plunger. Curves from a sine-shaped course of an eccentric press, the curves of toggle joint lever drives or component design-specific curves may be established. The plunger can be independently positioned, it can be braked at any location or accelerated and it may even be operated in an oscillating back and forth movement by reversing the eccentric between two points.
Such a servo press is disclosed, for example, in DE 10 2004 009 256 B4. The press described herein includes several servomotors which jointly operate a plunger. The servomotors act on the plunger via a drive which has a mass moment of inertia. This mass moment of inertia may be increased by an additional fly wheel, if desired. However, altogether the resulting mass inertia moment is selected so as to be less than that of conventional presses in which the fly wheel stores sufficient energy to complete a working stroke. It is rather so small that the servomotors can accelerate the fly wheel from a stand still and again brake it to a stand still. With such a design, it is possible to operate the presses on one hand in a reversing operation with variable strokes wherein, on the other hand, high press forces can be obtained with the aid of the fly wheel.
It is, however, a disadvantage of this solution that in spite of drive simplifications, complicated and costly movement transmission means in the form of gears are still needed. DE 41 09 796 C2 discloses an arrangement for pressing, bending and punching of metal work pieces wherein a servomotor acts directly on an eccentric. With this arrangement the stroke length, as well as the press forces, are to be changed a simple manner. In addition, by an axial guiding of the plunger, it's surface of contact with the workpiece is to remain unchanged. A disadvantage of this solution however is surely a limitation to very small press forces. For large deformation presses with several pressure points, such an arrangement is not suitable.
Based on this state of the art, it is the object of the present invention to provide a press having a press drive which on one hand is capable to generate high press forces with a variable plunger movement and, on the other hand is of simple design and cost effective.